I have a little tutorial here that can help you started with making those really nice, professional looking zinc frames for all your circular projects!
Here are several glass painting patterns that a great for practicing line tracing, inspired by nineteenth century photographs of Jane Burden Morris. I like those photographs because it's nice to see what was considered a great beauty in the days before heavy makeup and plastic surgery *wink*.
Here is a preview of some sketches for glass painting patterns I am currently working on. I have to work on the borders (the lines are just markers), and most of the faces could use improvement. I am aiming for a more "graphic arts" style - rather than purely representational.